German Patent 32 48 178 described a method for use with an offset printing machine in which digital image information is applied to a recording head which, selectively, causes melting of meltable substance particles located on a thermo transfer foil, so that the thermo transfer foil will have placed thereon a representation of the digital information in form of ink-accepting, i.e. oleophilic, and ink-repellent or, respectively, water-repellent, i.e. hydrophobic, and water-accepting, i.e. hydrophilic areas. The thermo transfer foil, which carries the information in point form, is then engaged against a printing cylinder for direct transfer of the information thereto.
The point-form energy application, specifically heat, corresponds to the electronic image information. An oleophilic or ink-accepting substance, coating the thermo transfer foil, is dissolved off, and applied to the printing cylinder. This system is complex since the transfer is in image point units, and can be applied, at any time, only to a single printing cylinder. The time taken to transfer the image to a printing cylinder is substantial due to the point-by-point transfer of the image information.
High-quality printing can be obtained by using cylinders having ink accepting receptors or cells. In a gravure printing system, the cylinder is formed with tiny receptor depressions or cells, located between a ridge pattern; in a screen printing system, the ink receptors are formed by the interstices between the screen filaments or elements. The receptors or cells can be formed by mechanical, electromechanical, electrothermal, or chemical material removal, in part, if desired, with intermediate photo-optic or chemical auxiliary processes. The receptors, to receive different quantities of ink, have different size, depth or spacing from each other. Methods to make gravure printing cylinders of this type, or screen cylinders with varying cell size or location, are expensive and complex, and must be carefully controlled. The numerous steps required thereby take much time and effort. Printing cylinders which, in large machines, can be unwielding and weigh up to several tons, have to be removed from the machine to make a new printing cylinder, in negative form. The imaging of these new cylinders, then, has to be carried out in large machines, and the then imaged cylinders have to be returned to the printing machines. Thus, gravure printing, although it provides high-quality printed subject matter, is economically suitable only if a very high number of copies or editions are required; likewise screens often are used to make many printed products.